How to "flatten" a multi-dimensional array to simple one in PHP?

In PHP, you can use the array_reduce function to flatten a multi-dimensional array. This function takes three arguments: the array to be flattened, a callback function that defines how to combine the elements, and an initial value for the accumulator. Here is an example of how to flatten a multi-dimensional array using array_reduce:

Example of flattening a multi-dimensional array with array_reduce in PHP

<?php

function flattenArray($array)
{
  return array_reduce(
    $array,
    function ($carry, $item) {
      if (is_array($item)) {
        return array_merge($carry, flattenArray($item));
      } else {
        $carry[] = $item;
        return $carry;
      }
    },
    []
  );
}

$multiDimensionalArray = [1, [2, 3], [4, [5, 6]]];
$flattenedArray = flattenArray($multiDimensionalArray);
print_r($flattenedArray);

Try it Yourself »

This will output:

Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 [5] => 6 )

Alternatively, you can use a recursive foreach loop with array_merge to flatten the array:

Example of flattening a multi-dimensional array in PHP

<?php

function flatten_array($array)
{
  $flat = [];
  foreach ($array as $value) {
    if (is_array($value)) {
      $flat = array_merge($flat, flatten_array($value));
    } else {
      $flat[] = $value;
    }
  }
  return $flat;
}
$multiDimensionalArray = [1, [2, 3], [4, [5, 6]]];
$flattenedArray = flatten_array($multiDimensionalArray);
print_r($flattenedArray);

Try it Yourself »

This will also output the same result as above.